Neurotrophic factors have an important role in supporting the survival, differentiation and function of neurons. By examining the actions of a specific neurotrophic factor, it should be possible to define essential features of the trophic relationship. This perspective may allow one to modulate neuronal survival and differentiation and, perhaps, to intervene in neurological disorders which threaten neuronal viability and function. Nerve growth factor (NGF) may be a trophic factor for cholinergic neurons of the basal forebrain. Death of these cells in Alzheimer's disease is thought to have an important role in memory loss. In this proposal we will further define the site and mechanism of NGF actions in the rat central nervous system (CNS) and will determine whether NGF supports the viability and differentiation of basal forebrain cholinergic neurons. NGF mediated induction of gene expression for the beta-amyloid precursor protein (APP) and the prion protein (PrP) will allow us to localize NGF-responsive neurons via in situ hybridization histochemistry. Radiolabeled probes will be applied to tissue sections to localize APP and PrP mRNA in individual neurons. We expect to see a response in forebrain cholinergic neurons; other populations may also respond. The mechanism of NGF actions on APP and PrP will be examined at the level of gene transcription and mRNA stability. These studies will examine NGF responses in basal forebrain in vivo and in pheochromocytoma (PC 1 2) cells in vitro. Agonists and antagonist NGF peptides will be prepared. In vitro assays will be used to characterize the potency and efficacy of peptides on neurite outgrowth and survival; their site of action will be examined in ligand-binding and affinity crosslinking studies. Potent, stable antagonists will be administered in vivo to attempt to block the actions of endogenous NGF. We expect to see inhibition of cholinergic neurochemical differentiation and decreased viability. NGF agonist peptides may stimulate cholinergic function. The proposed studies are expected to define key features of NGF actions in the CNS. They may suggest approaches for elucidating the actions of other CNS neurotrophic factors. Such studies may lead to new insights regarding the role of NGF and other trophic factors in neurodevelopmental and neurodegenerative diseases. The ability to deliver biostable neurotrophic agonists or antagonists may provide a means for treating such disorders.